1. Field of the Invention
The present invention relates to a heat resistant insulated wire and a method of preparing the same, and more particularly, it relates to a heat resistant insulated wire having excellent heat resistance which is applied to a solenoid, a transformer or a motor used in a high vacuum or under a high temperature, and a method of preparing the same.
2. Description of the Background Art
A heat resistant insulated wire may be applied to equipment such as heating equipment or a fire alarm, which must have safety under a high temperature. The heat resistant insulated wire is also employed in the environment of an automobile, the engine of which is heated to a high temperature. Such a heat resistant insulated wire generally comprises a conductor which is coated with heat resistant organic resin such as polyimide, polyamideimide, PEEK, fluororesin, PPS, aramid or polymaleimide, for example.
Japanese Patent Publication No. 61-7685 (1986) discloses a heat resistant insulated wire which is prepared by coating a conductor with an unmolten inorganic substance and an organic binder. After the organic resin is heated and thermally decomposed, ceramics still remains in this wire to maintain its insulativity.
However, the heat resistant organic resin which is employed for coating such a conventional heat resistant insulated wire cannot sufficiently withstand a high temperature.
For example, even the polyimide Upylex (product of Ube Industries, Ltd.) which is regarded as withstanding the highest temperature among heat resistant organic resin products can merely withstand 270.degree. C. at the most, and most of heat resistant organic resin products cannot be used under temperatures exceeding 250.degree. C.
In a heat resistant insulated wire comprising a conductor which is coated with an unmolten inorganic substance and an organic binder as disclosed in Japanese Patent Publication No. 57-12248 (1982), the organic binder is thermally decomposed and inorganic powder remains when the wire is used under a temperature exceeding the withstand temperature of the organic binder. After such decomposition, the coating film is in a porous state and its adhesion is reduced as compared with that in the initial stage, while fallout of the coating film is observed. When the organic binder is decomposed, further, a gas which is mainly composed of hydrocarbon may be generated to catch fire.